this project will analyze use of health care services (including drug abuse treatment) by Medicaid recipients in New Jersey with HIV disease who have injection drug use histories (IDU-HIV). Analyses will primarily use a research dataset which merges Medicaid claims and other state administrative data on a large statewide population which includes more than 6000 IDU-HIV as well as non-IDUs with HIV disease; previously-collected longitudinal interview data on a cohort of 267 persons with HIV/AIDS will also be used. The study will develop, improve, and apply methods for using claims data to study issues relating to the drug abuse-HIV connection and its impact on health care delivery, including the identification and analysis of spells of drug abuse treatment and non-treatment; the incidence of drug abuse-related health care events; indications of health care access barriers for IDU-HIV; and the consistency of use of HIV treatments in the IDU-HIV population. The project will examine the extent to which IDU-HIV receive drug abuse treatment and the predictors of drug treatment use; investigate how total cost of care, incidence and duration of hospitalization, incidence of emergency room care, utilization of home care services, frequency of outpatient contact, and other aspects of utilization differ among IDU-HIV in relation to demographic characteristics and participation in drug abuse treatment, and explore the extent to which individuals in drug abuse treatment and not in treatment experience health care episodes related to specific conditions for which IDUs are at special risk. It will investigate variations incidence and consistency of antiviral and prophylactic treatment among IDU-HIVs, and explore the impact of case-managed Medicaid care on IDU-HIVs. A variety of longitudinal data analysis techniques will be used to model utilization trajectories and transitions, including mixed-effects and multi-state transition models. This work will use data currently in hand to provide timely, critically needed information on health care delivery and access for IDU-HIVs and inform efforts to improve the way health care is provided to IDU-HIVs through Medicaid. It will also develop improved methods and measures for identifying drug-abuse related health services utilization in claims data, in order to enhance the future potential of linked claims data to address critical issues relating to HIV among drug users, including use of new antiviral therapies in this population.